1. Field of the Invention
The present invention relates to a process for preparing an aqueous emulsion and more particularly to a process for preparing an aqueous emulsion for use as an effective component of a water- and oil-repellent, etc.
2. Related Art
In the preparation of an aqueous emulsion by copolymerization reaction of a polyfluoroalkyl group-containing (meth)acrylic acid ester and stearyl (meth)acrylate, the copolymerization reaction is generally carried out by emulsion polymerization using a cationic emulsifier and a nonionic emulsifier, where stearyl (meth)acrylate cannot be emulsified without the cationic emulsifier. To facilitate the emulsification, it is well known from the following prior art to use an organic solvent such as acetone, a mixture of acetone and ethylene glycol, glycol ethers, glycol esters, etc.
JP-B-63-14027 discloses simultaneous use of dimethylalkylamine or its salt (cationic emulsifier) and a nonionic emulsifier in the homopolymerization or copolymerization of perfluoroalkylalkyl (meth)acrylate and also discloses addition of acetone to the polymerization system.
JP-B-2-25374 discloses copolymerization of the above-mentioned two kinds of monomers together with 2-hydroxy-3-chloropropyl (meth)acrylate to obtain an effective aqueous emulsion for a water- and oil-repellent, where the emulsion polymerization reaction is carried out in the presence of water and acetone together with both polyoxyethylene alkylphenol (nonionic emulsifier) and dimethylalkylamine acetate salt(cationic emulsifier).
JP-B-3-44593 discloses use of stearyltrimethylammonium chloride as a cationic emulsifier and a mixture of water, acetone and ethylene glycol as a reaction solvent in the invention disclosed in the above-mentioned JP-B-2-25374.
JP-A-5-263070 discloses copolymerization of the above-mentioned two kinds of monomers together with N-methylol acrylamide to obtain an effective aqueous emulsion for a water- and oil-repellent, where the emulsion polymerization reaction is carried out in an aqueous solution of dipropylene glycol monomethyl ether in the presence of both polyoxyethylene alkylphenyl ether (nonionic emulsifier) and alkyltrimethylammonium chloride (cationic emulsifier).
JP-A-6-17034 discloses copolymerization of the above-mentioned two kinds of monomers together with 2-hydroxyethyl acrylate and dimethyl acrylamide to obtain an effective aqueous emulsion for a water- and oil-repellent, where the emulsion polymerization reaction is carried out in a solvent mixture of water and a glycol ether-typed solvent such as dipropylene glycol monoethyl ether, etc. in the presence of both C.sub.16 H.sub.31 O(C.sub.2 H.sub.4).sub.30 H(nonionic emulsifier) and C.sub.n H.sub.2n+1 N.sup.+ H(CH.sub.3).sub.2.CH.sub.3 COO.sup.- (cationic emulsifier).
Simultaneous use of both nonionic emulsifier and cationic emulsifier in these emulsion polymerization reactions is based on the following grounds: when used as a water- and oil-repellent, polymer particles covered with a cationic emulsifier have a strong adsorption onto fibers and also have a good water- and oil-repellency. In the water- and oil-repellent treatment, usually an antistatic treatment using an antistatic agent comprising an organic or inorganic salt as the main component or a melamine resin treatment using a resin containing an inorganic salt as a catalyst are often carried out at the same time, where emulsion-breaking phenomena are often observed in the water- and oil-repellent treatment bath before application of the effective components to cloth, etc., when there are ionic components such as salts, etc., particularly anionic substances. This is also true in case of dyeing, where an anionic emulsifier as used to disperse the dye acts likewise.
When used in the preparation of an aqueous emulsion, an organic solvent has problems of not only worsening the working circumstance, but also contaminating the effluent water to increase its BOD and COD.
Therefore, to improve the anionic resistance of an aqueous emulsion prepared by using a cationic emulsifier and provide an aqueous emulsion complelety free from any organic solvent is indispensable for use of the emulsion as an effective component of a water- and oil-repellent.